Fix introspection data for builderAddCallbackSymbol. The callbackSymbol argument was marked as (scope async), which meant that it was safe to free after the first invokation, but this was not correct, and leads to crashes.

3.0.14

Update lower version bound on haskell-gi (>= 0.20.1).

3.0.13

Update nullable overrides to match gtk+ 3.22.11.

3.0.12

Fix a mistake in the introspection data in widgetGetParentwindow, where the return value was not properly annotated as nullable. Fixes #90.